This invention relates to compositions and methods for enhancing the spraying efficacy of exogenous chemicals used in spray-treating plants. An exogenous chemical, as defined herein, is any chemical substance, whether naturally or synthetically derived, which (a) has biological activity or is capable of releasing in a plant an ion, moiety, or derivative which has biological activity, and (b) is applied to a plant with the intent or result that the chemical substance or its biologically active ion, moiety, or derivative enter living cells or tissues of the plant and elicit a stimulatory, inhibitory, regulatory, therapeutic, toxic, or lethal response in the plant itself or in a pathogen, parasite, or feeding organism present in or on the plant. Examples of exogenous chemical substances include, but are not limited to, chemical pesticides (such as herbicides, fungicides, or insecticides), plant growth regulators, fertilizers and nutrients or mixtures thereof.
Various combinations of exogenous chemicals (e.g., foliar-applied herbicides) and surfactants or other adjuvants have been, and are currently, used, so that when water is added, the resulting sprayable composition is more easily and effectively retained on the foliage (e.g., the leaves or stems) of plants. Through this, and perhaps other effects, surfactants have been known to increase the biological effectiveness of herbicide compositions, or other compositions of exogenous chemicals, when added to, or included in, such compositions of exogenous chemicals. For example, the herbicide glyphosate (N-phosphonomethylglycine) has been formulated with surfactants such as polyoxyalkylene-type surfactants including, among other surfactants, polyoxyalkylene alkylamines. Surfactants have generally been combined with glyphosate or other exogenous chemicals either in a commercial concentrate or in a diluted mixture (e.g., a tank mix) that is prepared from separate compositions, one comprising an exogenous chemical (e.g., glyphosate) and another comprising surfactant, prior to use in the field.
Many exogenous chemicals are commercially packaged as a liquid concentrate that contains a significant amount of water. The concentrate is diluted by adding water in accordance with instructions. The prepared, dilute composition is then sprayed onto plants.
Some surfactants tend to degrade fairly rapidly in aqueous solutions. As a result, surfactants that exhibit this property can only be used effectively in tank mixes (i.e., mixed with the other ingredients in solution or dispersion in the tank soon before spraying is to occur), rather than being formulated in an aqueous composition with the other ingredients in the first instance. This lack of stability, or inadequate shelf-life, has hindered the use of certain surfactants in some exogenous chemical formulations.
Other surfactants, though chemically stable, are physically incompatible with certain exogenous chemicals, particularly in concentrate formulations. For example, most classes of nonionic surfactants, including polyoxyethylene alkylether surfactants, do not tolerate solutions of high ionic strength, as for example in a concentrated aqueous solution of a salt of glyphosate. Physical incompatibility can also lead to inadequate shelf-life. Other problems that can arise from such incompatibility include the formation of aggregates large enough to interfere with commercial handling and application, for example by blocking spray nozzles.
Two important application properties of a sprayable composition having exogenous chemicals and surfactants are its spray-dispersion particle-size distribution and the spray dispersion's adherence to the plants being sprayed. Small droplet-size dispersions tend to drift from the intended target plants so that larger droplet-size dispersions are preferred. While larger droplet-size dispersions drift less and deliver more composition to the plant, if the larger droplets adhere poorly to the foliage surface, the large droplets can aggregate on the foliage, causing a high variability in coating the foliage, or even run off the plant, wasting some of the composition and reducing cost-effectiveness of the spray method.
One consequence of the above-described variability in coating is that foliar-applied exogenous chemicals are typically applied at significantly higher rates than needed to give the desired biological effect in the particular situation where they are used, to allow for the natural variability that exists in efficiency of foliar uptake. A need therefore exists for sprayable compositions of exogenous chemicals that substantially remain on the contacted plant foliage and are efficiently uptaken and translocated, thereby allowing reduced use rates.
A need also exists for improved formulations of exogenous chemicals, particularly herbicides, that are stable and effective, coat foliage well, and for stable liquid concentrate formulations of exogenous chemicals that contain less water and more exogenous chemical than prior art concentrates.
Genetically modified crop plants (e.g., corn, soybeans) can be resistant to uptaken herbicides such as glyphosate so that an area having these plants plus undesirable weeds (e.g., lambsquarter, velvetleaf, giant ragweed) should be able to be spray treated with a glyphosate formulation so that only the weeds are eradicated. However, many formulations of glyphosate sprays inflict damage to the cuticle layer of the genetically modified crop plants, resulting in stress and reduced yield. There is, therefore, also a need for a herbicidal formulation that does not, or at least minimizes, damage to the cuticle layer of sprayed, desirable crop plants.